The long-term objective of this project is to examine the relationship between depression, dual diagnosis and medication adherence in HIV infected individuals. Understanding adherence behaviors in vulnerable populations is essential to maximizing the clinical effectiveness of highly active antiretroviral therapy (HAART) among all HIV seropositive populations. The specific aims of this study are (1) to describe the prevalence of depression and dual diagnosis (depression and substance abuse) in a cohort of 200 HIV infected individuals currently treated with HAART, (2) to describe the relationship between depression, dual diagnosis and antiretroviral adherence, (3) to examine the relationship between depression, dual diagnosis and response to a home-based nursing intervention to improve adherence to HAART. This is a prospective, descriptive study nested in a randomized clinical trial of a home-based nursing intervention to improve adherence to HAART (Williams, A.). Subjects will be 200 HIV infected individuals enrolled in the parent study. Measures of depression (self-report, Beck Depression Inventory, 5-item mental health subscale of the MOS Short Form) and substance abuse (self-report) will be added to the parent study data collection instrument and measured at baseline in face to face interviews. Adherence data (measured by self report, unannounced pill counts and MEMS cap data) will be collected at baseline, monthly for 3 months then every 3 months for 18 months.